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In this paper, a novel 3-D microheater has been developed in order to improve the performance of catalytic gas sensors. The 3-D microheater consists of a platinum heater embedded in a concave-shaped membrane which was formed in twice wet-chemical anisotropic etching with photoresist-spray-coating-based liftoff process. Based on the 3-D microheater, a catalytic gas sensor with a paired detector and compensator was developed by sol-gel process, introducing γ-Al2O3-supported 15-wt % Pd as catalyst. Finite element method analysis results suggest that sensitivity of the catalytic gas sensor can be improved by loading more catalyst on the active area and concentrating more combustion heat inside the concave-shaped membrane. Test results indicate that a high heating efficiency has been achieved. Power per active area of the 3-D microheater is only half or less than that of current 2-D microheaters. Sensor response to methane shows that the sensitivity to 50% lower explosive limit CH4 was 12 mV/ % CH4.